The distances separating Tyr-69 from the high-affinity nucleotide and metal binding sites in actin

The nucleotide binding site in actin was occupied with the fluorescent analogue formycin A 5' triphosphate which acted as a fluorescent donor for the acceptor chromophore dansyl chloride attached to Tyr-69. The distance separating the two chromophores was calculated to be 2.1 nm from the fluorescence energy transfer measurements. Similar measurements were made of the distances separating dansyl chloride, acting as donor, on Tyr-69 from Co2+ occupying the metal binding site. A distance of 2.1 nm was similarly obtained.